Triarylphosphates have established utility as functional fluids because of their plasticizer and lubricant properties. Particularly useful are "synthetic" triaryl phosphates prepared from mixtures of phenol and alkylphenols wherein the alkyl group contains 3 or 4 carbon atoms. Thus, triaryl phosphates such as isopropylphenyl/phenyl/phosphates and tertiarybutylphenyl/phenyl phosphates are prepared to have desirable properties of low color, viscosity, pour point, etc.
Conventional processes for forming triaryl phosphates employ two steps. The first step is alkylation of phenol with an olefin to give an alkylphenol feedstock. The second step employs heat and catalyst to phosphorylate the feedstock and yield a crude phosphate ester product. Depending on the intended use of the triarylphosphate, a third process step may be used to purify the crude product by distillation. Typical triarylphosphate synthesis and purification steps are described in U.S. Pat. Nos. Re. 29,540 and 4,139,487.
The prior art describes triaryl phosphate synthesis absent phosphorylation catalyst. For example, U.S. Pat. Nos. 1,425,392; 2,078,421; and 2,168,587 phosphorylate cresols, tertiary amyl phenols, and petroleum phenols at elevated temperatures.
The use of catalysts such as MgCl.sub.2 or AlCl.sub.3 in the phosphorylation step generally enhances reaction rate but subsequent removal of the catalyst is required in a purification step.
It is desirable to develop improved phosphorylation techniques for preparing triarylphosphates which will permit simpler and less costly purification.